Recent advances in printing press drying applications using infra-red equipment have led to higher powered systems. In many drying applications, for both ink and other heat sensitive coatings, press operations have increased to the extent that substrate speeds of 500 feet per minute are common. As a consequence, the surfaces of such substrates are irradiated or exposed to heat for only a very limited time. There has been a trend toward the use of higher specific output heating units. Lamps capable of up to 200 watts per inch of infra-red power are currently in use. Due to the physical limitations on space within most printing press housings, the drying apparatus must accomplish its purposes more rapidly than in the past and within the restricted available space. With the higher operating temperatures of the high powered lamps the resultant heat behind conventional heating units is easily 50 to 100 degrees Fahrenheit above ambient temperatures, which initiates a detrimental increase in heat in the vicinity of the drying units. As the heat accumulates around the dryers, the temperature rises in the final housing in which the drying equipment is located and backs up into the adjacent printing unit creating further problems. It is well known that changes of as little as 10.degree. F. to 15.degree. F. can significantly alter ink and coating viscosities, as well as affect water balance and alcohol content. The expansion and contraction of the dryer equipment leads to equipment failures. For example, many printing presses utilize chain driven continuous belts with grippers to feed the sheets by the dryers, and the spring loaded elements associated with such parts soften under the increasingly higher temperatures, creating further problems. Of course, when presses using infra-red drying apparatus are operated for long periods, e.g. three shifts per day, or during hot, high humidity conditions during the summer months the heating problems are compounded.
Currently presses with infra-red drying systems operate with higher powered lamps in one of several ways. Some presses are operated in the old manner without adequate cooling, and the equipment is shut down when higher temperatures create problems. More efficient presses have associated cooling systems that utilize either air or water cooling apparatus.
There has been a variety of prior art systems for dealing with the heat problems created by drying equipment. U.S. Pat. No. 3,825,407 to Y. Fujite et al. describes a reflector for reducing heat in a copying machine by the use of a reflector plate adjacent the heating elements. While the system employs no direct cooling of the reflector, loosely mounted brackets for the reflector permit thermal distortion to take place without damage to the reflector. U.S. Pat. No. 4,135,098 to H. Troue describes the use of a mercury vapor lamp with a reflector module to direct ultra-violet light to a coating on a moving substrate. The temperature of each reflector, which partially surrounds each lamp, is controlled by means of a water cooled heat sink spaced above the reflector so that only radiation heat transfer takes place between the reflector module surface and the heat sink. U.S. Pat. No. 4,143,278 to R. L. Koch, II, describes the use of a cooling pipe arrangement positioned between a substrate and downwardly open lamp assemblies, which have ultra-violet lamps for heating the substrate. In addition to the cooling provided by the pipe arrangement, ambient air is circulated to the dryer housing and is exhausted from the lower portion thereof. U.S. Pat. No. 4,408,400 to F. Colapinto, describes the use of a radiation type of heat exchanger which is positioned beneath the guide path of moving sheets to cool the unprinted underside of the passing sheets for the purpose of preventing any overheating.
The above mentioned prior art inventions have helped reduce some heating problems associated with specific drying apparatus. However, modern, multi-stage high speed presses which utilize infra-red heating lamps to dry coatings on moving substrates continue to be plagued with problems created by excessive detrimental heat build-up in the immediate vicinity of the heating lamps, in the housings where they are located, and in the adjacent press components.